Fig. 1: Drivers of ecosystem change and environmental response in five lakes on the Alaskan North Slope.

Environmental drivers: a Modelled temperature anomalies for the Arctic (blue filled circles)²⁹ and measured mean annual temperature at Barrow (open brown circles)⁶⁹. b Changes in nitrogen stocks in terrestrial ecosystem and soils at the Toolik LTER modelled by McKane et al.⁴⁷ (solid lines); and changes in nitrate concentrations measured in a Greenland ice core⁷⁰ (green filled circles). Limnological response: c Mean lake-wide carbon burial in the five study lakes integrated by decade (grey fill); and z-scores for carbon: nitrogen ratios (open squares) and carbon isotopic composition (filled black circles) in master cores from the same five lakes. Fitted trend lines and 95% confidence intervals (shading) from a general additive model (GAM). d z-scores for biogenic silica (BSi) (open circles) and axis-1 scores from a PCA ordination of fossil diatom assemblages (green filled circles) for cores from two of the study lakes. Fitted lines and confidence intervals from GAMs. e z-scores for nitrogen isotopes in cores with increasing (Perfect, Forgetful; blue symbols) and decreasing (Surprise, Relaxing; red symbols) trends. GAM trend lines and confidence intervals as in Panels c and d. For the environmental response variables in the sediment-core records, two time-lines of major ecological change (vertical lines), the first beginning around 1880 (carbon burial and stable isotopes) and the second ~1970 (diatoms and biogenic Si) are based on breakpoint analysis (see “Methods” and Supplementary information).